Experimental and theoretical investigation of the structural, chemical, electronic, and high frequency dielectric properties of barium cadmium tantalate-based ceramics

Single-phase Ba (Cd13 Ta23) O3 powder was produced using conventional solid state reaction methods. Ba (Cd13 Ta23) O3 ceramics with 2 wt % ZnO as sintering additive sintered at 1550 °C exhibited a dielectric constant of ∼32 and loss tangent of 5× 10-5 at 2 GHz. X-ray diffraction and thermogravimetric measurements were used to characterize the structural and thermodynamic properties of the material. Ab initio electronic structure calculations were used to give insight into the unusual properties of Ba (Cd13 Ta23) O3, as well as a similar and more widely used material Ba (Zn13 Ta23) O3. While both compounds have a hexagonal Bravais lattice, the P321 space group of Ba (Cd13 Ta23) O3 is reduced from P 3 m1 of Ba (Zn13 Ta23) O3 as a result of a distortion of oxygen away from the symmetric position between the Ta and Cd ions. Both of the compounds have a conduction band minimum and valence band maximum composed of mostly weakly itinerant Ta 5d and Zn 3dCd 4d levels, respectively. The covalent nature of the directional d -electron bonding in these high- Z oxides plays an important role in producing a more rigid lattice with higher melting points and enhanced phonon energies, and is suggested to play an important role in producing materials with a high dielectric constant and low microwave loss.